In cell based mobile communication systems base stations are provided to communicate with the mobile devices. Such base stations usually have a high frequency radio part, called Radio Equipment (RE), which RE is controlled by a further part called Radio Equipment Controller (REC). The REC may be located in the base-station cabinet, while the RE is usually located near the antennas. An interface between both parts has been standardized, and is called Common Public Radio Interface (CPRI).
The standard “Common Public Radio Interface (CPRI); Interface Specification V5.0 (2011, Sep. 21)”, as provided on http://www.cpri.info, describes the interface, abbreviated CPRI V5. An older version of the CPRI is “Common Public Radio Interface (CPRI); Interface Specification V4.2 (2010, Sep. 29)”, also provided on http://www.cpri.info, abbreviated CPRI V4, defines an earlier version of the interface. In general, sub-versions of the CPRI V4 or V5 are denoted as V4.x or V5.x.
The Common Public Radio Interface (CPRI) configuration consists of multiple Radio Equipment Controllers (REC) and multiple Radio Equipments (RE) connecting point to point in a chain network using very high frequencies (up to 9.8 GHz). Data samples are received at the RE and interfaced via an IQ data link to the REC, in a data format based on the I and Q components of the modulated signal. Besides IQ data link, CPRI supports further types of communication and management (C&M) data: a Vendor Specific (“VSS”) channel, a HDLC (“slow C&M channel”) and an Ethernet link (“fast C&M channel”).
FIG. 1 shows an example of CPRI connectivity. The Figure shows an example of a base station architecture 100 comprising a CPRI interface 101 between a REC 102 and an RE 103. A further CPRI interface 104 may be provided to interconnect multiple REs. As such, the CPRI interface is described in the CPRI V5 and chapter 2 describes the CPRI related parts of the basic radio base station system architecture. The Figure is taken from chapter 2 (see CPRI V5, FIGS. 2 and 2A on page 10) and is further described in chapter 2.2 System Architecture of the CPRI standard.
It is noted that existing CPRI controllers in baseband processing (Layer 1 processing) chips may support CPRI V4.x or former versions. CPRI V4.x supports the following telecommunication standards: WCDMA, LTE and WiMAX, but it does NOT support the legacy GSM communication standard (Global System for Mobile Communications), which is the well known standard set developed by the European Telecommunications Standards Institute (ETSI) to describe protocols for second generation (2G) digital cellular networks used by mobile phones, i.e. the de facto global standard for mobile communications. CPRI V5.x is a newer standard (from late 2011) which enhanced the CPRI to support GSM as well. However, there are many existing systems that have GSM infrastructure installed. In such systems, which use the current processors with CPRI 4.x support only, GSM support is lacking.